Traditional heating and cooling systems have been quite simple in commercial and residential buildings. For example, a heating system consisted of a central heating unit that connected to a distribution network of vents or pipes distributed throughout the structure. To control the central unit, a thermostat is located in the temperature control area with a manually adjusted setpoint to call for a higher or lower temperature. As technology advanced, systems became more complex such as shown in U.S. Pat. No. 5,024,265 issued to Bucholz et al. on Jun. 18, 1991, U.S. Pat. No. 5,971,284 issued to Hammer on Oct. 16, 1999, and U.S. Pat. No. 6,711,471 issued to Kidder on Mar. 23, 2004.
The simplest hydronic multi-zone heating systems using non-communicating thermostats simply turn on a boiler and circulators whenever any thermostat calls for heat. The boiler target is set to a fixed value sufficient to meet heating requirements during the coldest days of the year. This system is inefficient in that it results in a boiler maintaining temperatures that are much higher than required for heating during most of the year.
One improvement is to install an outdoor reset control on the boiler. When an outdoor reset control is installed, the boiler operates at a target temperature that is calculated based on the current outdoor temperature. Thus, high targets are calculated during cold outdoor temperatures and lower targets are calculated during mild outdoor temperatures. Controls typically include settings for a minimum target, a maximum target, and the amount of target change vs. outdoor temperature change (known as the “heating curve”).
The disadvantage of these outdoor reset systems is the requirement of a first sensor to measure and supply temperature, a second sensor to measure the outdoor temperature, and the configuration of several settings to operate properly. Further, the heating requirements for a given area may differ depending on a number of factors, such as size of the area, insulation of the area, heat generated by people and appliances, and radiant heat from the sun on the outside of the building, to name a few. Therefore relying solely on outdoor thermostats to calculate a boiler target temperature can result in a target temperature that is lower or higher than necessary, again creating an inefficient system and/or discomfort.